Preparation of silver halide emulsions



Un t Stat s P t 2,976,150 PREPARATIDN on SILVER HALIDE EMULSIONS No Drawiug.- Filed Oct. 16, 1957, Ser. No. 690,438

7 Claims. (Cl. 96-94) This invention relates to the preparation of photographic silver halide emulsions. More particularly it relates to a method of preparing photographic silver halide emulsions by the precipitation and growth of silver halide grains in a solution of a cationic ampln'philic polyalkylene oxide compound. Still more particularly the invention is directed to the coagulation of silver halide grains so dispersed with an anionic long chain compound or an anionic polymeric compound washing said grains and the redispersion of them in a natural or synthetic polymeric binder.

Weaver US. Patent 2,752,246, issued June 26, 1956, relates to aprocess which comprises precipitating silver halide in an aqueous solution of a non-ionic amphiphilic polyethylene oxide surface active agent. The process is stated to produce a substantial proportion of flat, geometric shaped grains similar to those formedin the presence of gelatin. The process, of course, avoids the many disadvantages of gelatin. For example, from a physical standpoint gelatin is brittle and very susceptible to humidity changes. It is also susceptible to mold, bacteria, etc. The above process also has the advantage of enabling the worker to more easily control the inherent sensitivity of the grains as well as being able to more elliciently sensitize said grains with optical and non-opti cal sensitizing agents. This also allows for more control, particularly of the fog level of the emulsion which is often a problem when sensitizing in the presence of gelatin. By being able to carry out all of the operations on the silver halide grains including their initial formation in the absence of gelatin, much greater reproducibility of photographic characteristics is obtainable. It is also possible to use more photographically inert colloid binder than was previously possible.

In the process of the Weaver patent, after precipitation and growth of the silver halide grains, they are separated from the aqueous medium and washed free of soluble salts by conventional methods, e.-g., decantation or centrifugation. This washing operation, on a large scale, is usually carried out by gravity sedimentation of the grains and requires several hours. Such a method of removing soluble salts is not only time consuming but is also inefiicient. Centrifugation accelerates the sedimentation but it also tends to agglomerate the grains in such a way that redispersion is extremely difficult if not impossible. In addition to the above disadvantages, this method of washing also entails a high loss of silver halide. Of course, other disadvantages are present in the conventional processes using gelatin as the dispersing agent where chilling to set the emulsion and lengthy washing procedures are customary.

An object of this invention is to provide an improved process for the preparation of silver halide emulsions. Another object is to provide such a process which gives uniform, dependable results during large scale operations. Yet another object is to provide a process for forming uniform dispersions of flat, well-shaped geometric silver halide crystals in water-permeable organic colloids which 2 dispersions are free from agglomerates. Still other objects will be apparent from the following detailed description of the invention.

The aforesaid disadvantages of prior art processes are overcome and the above objects attained in accordance, with the invention by forming (i.e., precipitating), and ripening silver halide grains in an aqueous solutionof it cationic amphiphilic polyalkylene oxide compound taining at least two intralinear -CH CH O gm 5 and a saturated aliphatic hydrocarbon radical of atv 8 carbon atoms. No colloid binder is or need, be p I", ent during this operation. The silver halide grains are coagulated by addition of an'aqueous solution of (a)- an anion soap, e.g., an anionic surface active agefn'tv con; t aining an aliphatic hydrocarbon radical of at least 12 carbon atoms and a single ionizable group, such assodium dodecyl, tetradecyl, hexadecyl or octadecyl sulfate and the corresponding sulfonates, or (b) an anionic poly: meric material containing a plurality of ion'izable groups, e.g., those specific ones listed in Moede US. Patent 2,772,165, Nov. 27, 6, and in assignees Moede U.S.

application Ser. No. 454,213, filed Sept. 3, 1954 (Patent No. 2,863,769, patented December .9, 1958,), lowering the pH. Rapid sedimentation occurs and wash ing may be carried out by decantation. The grains are redispersed by adding water, raising the pH and agitat ing. The pH values necessary for coagulation. and redis} persion depend on the dissociation constants of the eat ionic compounds and anionic coagulating reagents. can vary over a wide range. In certain cases sedimenta-j tion will occur at any pH value but redispersion can achieved by addition of a water-permeable organic corloid binder. The organic collod may be either a naturally occurring colloid, e.g., gelatin, albumin, casein, or a synthetic organic colloid, e.g., polyvinyl alcohol and its esters and acetals. Sensitization of the emulsion w th optical and non-optical sensitizing compounds may carried out before or after the addition of the waterpermeable colloid binder. Centrifugation is not neces sary nor desirable because sedimentation is so rapid and; in fact, here centrifugation causes difiicultly redispersi'ble agglomerates.

The photographic emulsions prepared from the silver halide grains obtained by the process of this invention have good photographic quality and are suitable for editing on conventional photographic supports, e.g., trails parent film base, glass plates, metal sheets, cloth and paper.

To be more specific, silver halide grains suitable for producing light-sensitive dispersions or emulsions, in new; ral or synthetic water-permeable colloid binders are pre: pared in an aqueous solution of a cationic amphipliilie polyethylene oxide compound having thergeneral formula R-ILI-(CH2CH2O)DH where R' is a hydrophobic group including a saturated aliphatic hydrocarbon radical of at least 8 carbon at oms; R is hydrogen, an alkyl group of from i to "18 carbon atoms, a radical of the formula -(CH CH O),,,H p where m is an integer from 1 to 20, or a cycloalkyl 'r'adi cal, and n is an integer greater than 2. The aqueous solution may contain from 1 to 30%, preferably 2 it; 20% by weight based on the weight of the silver halide, of the cationic amphiphilic oxyethylene compound. I

An important class of the above cationic amphiphilie polyethylene oxide compounds are the-condensation products of ethylene oxide with an N-monoalkylaniline, with or without an alkyl substituent in the benzene nucleus, wherein the N-alkyl group contains at least 8 carboii atoms, and said condensation products contain at least i 3, or an average of at least 3, oxyethylene groups. These condensation products can be represented by the general formula (CHzCHrO) H R1 where X is hydrogen or an alkyl radical of 1 to 18 carbon atoms, R is an alkyl radical of 8 to 18 carbon atoms and n is a positive integer of 3 to 25 or more. Suitable radicals for X include methyl, ethyl, propyl, butyl, pentyl, hcptyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, and ,octadecyl, and R may be any of such radicals which have 8 or more carbon atoms.

The condensation products having the formula set forth in the preceding paragraph can be prepared in accordance with the exemplary procedure given below from aniline, an alkyl bromide of 1 to 18 carbon atoms, e.g., octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, heptadecyl and octadecyl bromide, and ethylene oxide.

EXEMPLARY PROCEDURE Two molar parts of alkyl bromide, e.g., n-dodecylbroinide, were treated with 1500 parts of aniline and the mixture was allowed to stand overnight. A deposit of crystalline aniline hydrobromide was removed by filtration and the filtrate was heated to 120l30 C. for 3 to 4 hours to carry the reaction to completion (the aniline hydrobromide, removed by filtration above, was washed with acetone, the acetone evaporated, and the residue added to the main batch before the 3-4 hours heating period). The material was then washed 2 or 3 times in a separatory funnel with approximately 500 ml. portions of 20% sodium hydroxide solution to remove all hydrogen bromide.

The organic layer was distilled at atmospheric pressure through a short column to remove the excess aniline. The distillation was carried out until the pot temperature reached 290 C. The pot residue was transferred to a vacuum still and distilled to purify the N- alkylaniline formed. The distillation was carried out at a pressure of about 50 microns to yield 80-95% of the theoretical quantity of the N-alkylaniline.

One molar part of the purified N-alkylaniline and 2 ml. of boron trifluoride/diethyl ether complex were placed in a flask which was flushed with nitrogen gas to remove all oxygen. Ethylene oxide gas was then bubbled through the liquid at such a rate that good agitation was produced. The temperature of the mixture rose rapidly to about 100 C. and then gradually returned to room temperature. The contents of the flask were then heated to 140150 C. while a gentle stream of nitrogen was passed through the flask to remove volatile substances, and after being cooled the product was transferred to a high vacuum still. This product was distilled at a pressure of about 50 microns to give a yield of 85-90% of tlhe theoretical amount of the 2-(N-alkylanilino)ethano One molar part of the purified 2-(N-alkylanilino)ethanol was placed in an appropriate vessel, one-half part of freshly cut sodium was added, the vessel was flushed with a stream of nitrogen gas and the contents were heated to 140-150 C. in a stream of nitrogen until all of the sodium had dissolved. Ethylene oxide was then introduced until the weight gain indicated the absorption of the desired quantity of ethylene oxide. The product of this reaction, depending upon the alkyl halide used in the preparation of the alkylaniline, and also depending on the amount of ethylene oxide allowed to condense with the 2-(N-alkylanilino)ethanol, is the desired product of the above general formula.

After the grains have reached the desired shape and size, which can be determined by microscopic examination, an aqueous solution of an anionic material, for instance, an anionic polymer, e.g., the sodium o-sulfobenzaldehyde acetal of polyvinyl alcohol, is added containing about half the quantity of acetal coagulating agent as there is dispersing agent used for the precipitation and dispersion of the silver halide grains. The pH of the solution is lowered to produce coagulation. After sedimentation the supernatant liquid is decanted and washing can be carried out by addition of water which is then decanted. The grains are redispersed by the addition of water and by raising the pH value. Sensitization may then be carried out, followed by addition of a water-permeable colloid binder having protective colloid properties, e.g., gelatin, casein, albumin, synthetic protective colloids, e.g., polyvinyl alcohol, low substituted polyvinyl acetals, e.g., formaldehyde, acetaldehyde, isobutyraldehyde, benzaldehyde and p-hydroxybenzaldehyde; polyvinyl acetals containing sufiicient intralinear CH CHOH- groups to render them hydrophilic; polyvinyl acetal color formers, water-soluble polyamides and water-soluble cellulose derivatives.

The invention will now be illustrated in and by the following examples wherein the parts and percentages are by weight unless otherwise indicated. T hese examples were carried out under darkroom" conditions in the absence of significant actinic radiations which would xpose the emulsions prior to use of the coated photographic elements.

Example I An aqueous solution of 350 ml. of 3 N silver nitrate, and 1500 ml. of distilled water was mixed with an aqueous solution of 300 ml. of 3 N ammonium bromide, 15 ml. of 0.5 N potassium iodide, 200 ml. of a 10% aqueous solution of an N-dodecyl aniline polyethylene oxide condensation product predominating in a compound having the structure:

phenylN 0121125 and 500 ml. of distilled water. After 10 seconds 150 ml. of a 20% aqueous solution of ammonium hydroxide were added to the mixture in 5 seconds. The emulsion was ripened at F. for 5 minutes and then treated with 100 ml. of glacial acetic acid in 5 seconds.

To the ripened emulsion was added 100 ml. of an 8.8% aqueous solution of polyvinyl alcohol which had 30% of the hydroxyl groups acetalyzed with sodium 0- sulfobenzaldehyde. The emulsion was then acidified with 3 N sulfuric acid to reduce the pH to 3.5. The temperature of the emulsion was adjusted to 85 F. and the resulting coagulum allowed to settle. Most of the silver halide grains settled in a few minutes but the settling time was extended to 20 minutes.

The supernatant liquid was poured off and the coagulum was redispersed in 100 ml. of distilled water and enough 3 N sodium hydroxide to maintain the pH at 8. 0 to 8.5 using vigorous mechanical agitation at F. One-fifth of the redispersed emulsion was stirred into 200 g. of a 10% aqueous gelatin solution, treated with 6 ml. of a 10% aqueous solution of C-cetyl betaine (wetting agent) adjusted to 500 g. with distilled water and a pH of 9 with 3 N NaOH. After the addition of 10 ml. of a 50% alcoholic solution of di-isopropanolamine, the emulsion was coated on a film base support to yield a smooth coating having a coating weight of 80 mg./sq. dec. based on the weight of silver halide.

The dried coating was exposed in a positive 113 sensitometer described in Mees Theory of Photographic Process, p. 789), and developed 4 minutes at 68 F. in a developer of the following composition:

Grams N-methyl p-aminophenol hydrosulfate 0.5 Hydroquinone 3.4 Sodium sulfite (anhydrous) M 28.0 Sodium carbonate (anhydrous) 10.0 Potassium bromide 0.4

Water to make 1.0 liter.

A solution of 50 ml. of 3 N aqueous silver nitrate was treated with 20% aqueous NH OH until the precipitate which first forms was completely redissolved. The resulting solution, together with 312 ml. of distilled water, was mixed with a solution of 72 ml. of 3 N aqueous ammonium bromide, 4 ml. of 0.5 N aqueous potassium iodide, 39 ml. of a solution of a mixture of N-alkyl di-polyoxyethylene glycol amines, the alkyl groups of which are composed of from 16 to 18 carbon atoms and the polyoxyethylene glycol groups contain from 13 to 16 ethylene oxide groups and 18 ml. of water. The dispersion was stirred for 30 minutes at room temperature, and the pH adjusted to 6.5 with acetic acid. The mixture was then treated with 10 ml. of a 10% aqueous solution of the partial acetal of polyvinyl alcohol and orthosulfobenzaldehyde set forth in Example I. Stirring was continued for 5 minutes and then terminated. Coagulation and settling occurred in about 2 minutes to give a clear supernatant liquid. This supernatant liquid was decanted. Anaqueous solution of 10 ml. of l N KOH and 78 of distilled water was then added and redispersion of the silver halide grains occurred in a satisfactory manner. The resulting dispersion was suitable for incorporation in an organic protective colloid binder solution, e.g., gelatin, polyvinyl alcohol, etc. as described in Example I.

Example III An emulsion was made according to Example H using as the dispersing agent for the silver halide grains a cationic amphiphilic condensation product of N-dodecylaniline with ethylene oxide predominating in a product having the formula:

(31213125 in an amount of 5 ml. of a 10% solution in place of the alkyl di-polyoxyethylene glycol amine. Upon adjustment of the pH to 4 with acetic acid and the addition of the polyvinyl acetal of Example I, the emulsion coagulated in about 5 minutes. After decantation, addition of water and elevation of the pH to 7, the silver halide grains became completely redispersed and they were suitable for conversion to a photographic emulsion by the addition of an aqueous solution of an organic protective colloid binder, e.g., gelatin or polyvinyl alcohol.

Example IV Example V An emulsion was made according to the procedure described in Example [I except that the dispersing agent had the general formula RNH---(CH CH O) H where R is a tertiary alkyl group having from 18-24 carbon atoms and n is an average. of 25 and was made from a mixture of primary amines having molecular weights of 269325, a neutral equivalent of 315, and a boiling range of 265-305 C. (760 mm.). This agent was used in an amount of 39 ml. of a 10% aqueous solution. The pH was adjusted to 4.0 with acetic acid and upon addition of 100 ml. of an 8.8% solution of the anionic polyvinyl acetal of Example I the emulsion coagulated in about 5 minutes. The silver halide grains, after decanting the supernatant liquid and washiug by further decantationto remove soluble salts, were redispersed by the addition of water and adjusting the pH to 9,2. Theresulting persion was suitable for mixing with a solution of a protective colloid binder to form a photographic emulsion.

Example VI An emulsion was made as described in Example but with an ethylene oxide condensation product with a tertiary-alkyl amine as the dispersing agent, said product predominating in compounds having the structure: RNII-(CH CH O') 15 H where R is a mixture. of tertiary alkyl groups having from 18 to 24 carbons of the type described in Example V. The dispersing agent used in an amount of 39 ml. of a 10% aqueous solution. The pH of the silver halide dispersion was adjusted to 4.0 with acetic acid and ml. .of an 8.8% aqueous solution of the anionic sodium o-sulfobenzaldehyde polyfvinyl acetal of Example I was added. Coagulation and settling occurred in about 5 minutes. Redispersio'n of the silver halide grains was obtained by the addition of water and adjustment of the pH to 9.2 after decantation washing to remove soluble salts. The resulting dispersion of silver halide grains was suitable for mixing with pro: tective colloid binder solutions to form photographic silver halide emulsions.

Example VII An emulsion was made accordingto Example 11 but using a cationic amphiphilic dispersing agent comprising the condensation product of octadecyl aniline with an yleneoxide predominating in a compound having the structure:

(onion-,omrr

The dispersing agent was added in amount of 20 of ii 5% aqueous solution. The pH was adjusted to 3.0 with acetic acid. Upon addition of 100 ml. of an 8.8% aqueous solution of the sodium o-sulfobenzaldehyde polyvinyl acetal ofExample 1 coagulation and settling took place within about 5 minutes. The supernatant liquid was decanted andthe coagulum was washed with water to remove the soluble salts. Redispersion was brought about by adding water and adjusting the pH to 7.0 with potassium hydroxide. The resulting dispersion was suitable for mixing with a solution of an organic protective colloid binder, e.g., gelatin or polyvinyl alcohol, to form a photographic silver halide emulsion.

Example VIII Example VII was repeated using in place. of the pound of that example a condensation product of octadecylaniline with ethylene oxide, said product predominating in a compound of the following structure:

(CHQCHzOhuH phenyl-N CrsHav The compound was used in an amount of 20 ml. of a 5% solution. A silver halide dispersion was obtained after coagulation in the manner shown in that example which was suitable for making a photographic emulsion.

Example IX The dispersing agent was added in an amount of 20 ml. of a aqueous solution. The pH was adjusted to 3.0 with acetic acid. After coagulation as described in Example 11 and decantation of the supernatant liquid, the emulsion was washed by decantation to remove the soluble salts. The silver halide grains were then redispersed by adding water and raising the pH to 7 with potassium hydroxide. The dispersion was suitable for making a photographic silver halide emulsion as described in preceding examples.

Example X An emulsion was made as in Example 11 using ml. of a 10% aqueous solution of the alkylamino compound of that example and as the anionic coagulating agent 20 ml. of a 5% aqueous solution of sodium dodecyl sulfate. The coagulating agent was added after the pH was adjusted to 6.0 with acetic acid. The coagulum settled out in about 5 minutes and after decantation of the supernatant liquid the silver halide grains were redispersed in 10% solution of gelatin and the pH adjusted to 10 with potassium hydroxide. The resulting dispersion was suitable for preparing a light-sensitive photographic silver halide emulsion as described above.

Example XI An emulsion was prepared as in Example X using 10 ml. of a 10% aqueous solution of the dispersing agent used in Example 11. Coagulation was achieved by the addition of 20 m1. of a 5 aqueous solution of the sodium salt of the sulfate ester of p-nonylphenyl tetraethylene oxide. The emulsion settled out within about 5 minutes. After decantation of the supernatant liquid, the coagulum was redispersed in a 10% solution of gelatin wherein the pH was adjusted to 7 with potassium hydroxide. The resulting dispersion was suitable for coating as a lightsensitive photographic emulsion.

Example XII The above example was repeated using 80 ml. of a 10% solution of the same dispersing agent and 80 ml. of the 5% aqueous solution of the sodium salt of the sulfate ester of Example XI with similar results.

The invention has been illustrated in the examples with certain specific cationic amphiphilic polyalkylene oxide compounds. However, the process is not limited to the use of these specific agents but can be carried out with any of the condensation products having at least 2 moles of alkylene oxide having 2 to 3 carbon atoms, i.e., ethylene and propylene oxides, with a secondary or tertiary amine having a replaceable hydrogen attached to I nitrogen which in turn is attached to at least one hydrophobic hydrocarbon group. Among the particularly useful compounds are those which are condensation products of 10 to 20 moles of ethylene oxide with primary and secondary amines, e.g., compounds described in U.S. 1,970,578. The proportions of cationic dispersing agent used in preparing the silver halide dispersions of this invention, as indicated above, may be from 1 to 30% of the weight of the silver halides.

Other useful anionic surface active materials which can be used in the coagulation step include (a) the sodium, potassium and ammonium salts of alkylsulfonic acids of 10 to 18 carbon atoms including all of the homologous salts within this range as well as mixtures of two or more of such compounds, (b) any of the sodium, potassium and ammonium salts of sulfated primary aliphatic alcohols of 10 to 18 carbon atoms, (0) the sodium, potassium and ammonium salts of sulphated secondary alcohols containing at least 8 carbon atoms in the molecule. Specific useful compounds of this type and other useful anion soaps are described in Waller et al. U.S. Patent 2,489,341 of Nov. 29, 1949. Suitableanionic polymers are disclosed in the Moede patent and applications referred to above, including those of U.S. Patents 2,462,527,

and n is an integer greater than 2,

2,609,290, 2,609,360 and 2,533,210 and in German Patent 643,650. Preferred such anionic polymer coagulants are the water-soluble, acid-soluble organic anionic polymers of high molecular weight (i.e., in excess of 10,000) which contain periodically occurring groups taken from the class consisting of free acid groups and alkali metal salts thereof.

This invention provides a new process of preparing silver halides for photographic purposes. The process is especially useful in the preparation of silver halides to be used in photographic emulsions wherein the main water-permeable organic colloid binder is a synthetic compound or mixture of compounds such as polyvinyl alcohol and polyvinyl acetal. Heretofore, it has been ditficult to prepare such emulsions with sufficient sen sitivity to be acceptable because satisfactory silver halide grain growth in the synthetic colloids is difficult to achieve. In the present process, silver halide grains having the desired size for optimum photographic sensitivity are first prepared and then added to the desired binder. The process offers several advantages when used in the preparation of conventional gelatin emulsions. By employing the process of the invention it is not necessary to disperse silver halides in gelatin, then chill the gelatin dispersion and shred it to remove the soluble salts in the conventional time-consuming manner. The process also avoids the loss of silver halide and the time-consuming procedures of the prior art processes using non-ionic surface active dispersing agents.

What is claimed is:

1. A process for preparing light-sensitive silver halide grains which comprises precipitating and ripening lightsensitive silver halide grains in an aqueous solution containing as the sole organic constituent a cationic amphiphilic polyoxyalkylene compound of the formula where R is a hydrocarbon group taken from the class consisting of phenyl and saturated aliphatic hydrocarbon radicals of at least 8 carbon atoms, R is a member taken from the group consisting of hydrogen, alkyl of l to 18 carbon atoms, cycloalkyl and a radical of the formula -(CH CH O) I-I where m is an integer from 1 to 20 lowering the pH to produce coagulation, coagulating said grains by the addition to the resulting aqueous solution of an aqueous solu tion containing a water-soluble anionic surface active agent containing a hydrophobic group and an ionizable group and taken from the class consisting of (a) anion soaps containing an aliphatic hydrocarbon radical of at least 8 carbon atoms and an ionizable group taken from the class consisting of sulfonic acid and sulfuric acid and their alkali metal and ammonium groups and (b) watersoluble, acid-soluble organic anionic polymers of molecular weight greater than 10,000 containing a plurality of periodically occurring ionizable groups taken from the class consisting of free acid groups and alkali metal salts thereof, and washing the silver halide grains which settle out.

2. A process as set forth in claim 1 wherein said polyoxyalkylene compound is a condensation product of an N-monoalkylaniline with ethylene oxide.

3. A process as set forth in claim 1 wherein said polyoxyalkylene compound has the formula komornopn is an alkyl radical of 1 to 18 carbon atoms and R is an atoms.

"4. A process'as set forth in claim 1 wherein said surface active agent is a sodium alkyl sulfate of 10 to 18 7. A process as set forth in claim 1 wherein said col-- carbon atoms. loid is gelatin.

5. A process as set forth in claim Wh c said References Cited in the file of this patent face active agent is a water-soluble, and-soluble polyvmyl acetal of an aldehyde containing recurring sulfonic acid 6 UNITED STATES PATENTS sodium salt groups. 2,146,873 Wilmanns Feb. 14, 1939' 6. A process as set forth in claim 1 wherein the washed 2,161,322 Steindorfi et a1 June 6, 1939 grains are redispersed in an aqueous solution containing 2,527,261 Hart et a1. Oct. 24, 1950 a water-permeable colloid having protective colloid prop- 2,752,246 Weaver June 26, 1956 erlies. 10 2,772,165 Moede Nov. 27, 1956 

1. A PROCESS FOR PREPARING LIGHT-SENSITIVE SILVER HALIDE GRAINS WHICH COMPRISES PRECIPATING AND RIPENING LIGHTSENSITIVE SILVER HALIDE GRAINS IN AN AQUEOUS SOLUTION CONTAINING AS THE SOLE ORGANIC CONSTITUTION A CATIONIC AMPHIPHILIC POLYOXYALKYLENE COMPOUND OF THE FORMULA 